I hope this one comes across as a Superman movie, moreso than a quirky Guardians flick.
I don't feel like the inclusion of Guy Gardner, Mr. Terrific, Metamorpho and Hawkgirl (as main castmembers) into Superman's debut film is necessary. Feels like Gunn just needed his usual group of losers and misfits to tell his underdog story.
If you want to contrast Superman's ideology to another 'white knight' who wants to save the world through less virtuous means, you've got that with Lex Luthor. Almost like
Matt and Fisk both wanting to 'save the city' in DD S1.